Long-term interannual temperature variability across the KwaZulu-Natal Bight as a technique for monitoring the complex uThukela Marine Protected Area, South Africa

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The uThukela Marine Protected Area (MPA), situated on the continental shelf of the KwaZulu-Natal (KZN) Bight on the northeastern coast of South Africa, has been identified as a vital ecological region. Knowledge of the oceanographic dynamics in the region is essential for understanding the functioning of the ecosystem and the effectiveness of the MPA. This study analysed ocean temperature variability at 20 sites across the KZN Bight, between 1980 and 2021, using in situ and satellite data. Significant warming of an average of 0.03 °C y−1 across the period occurred at sites within and around the MPA. Coastal sea surface temperatures warmed by an average of 0.02 °C y−1, during both summer and winter. However, a persistent decrease in temperatures along the length of the KZN Bight during the summer of 2017/2018 could have significant consequences for temperature-sensitive species. Significant coastal temperature variability during the period 1980–2021 was not reflected in a data subset covering 2013–2021, highlighting the importance of long-term spatially extensive monitoring when investigating climate change within MPAs. Warming biases of up to 2 °C and an underestimation of the warming rates observed in satellite-derived temperatures highlight the limitations of using remotely sensed observations to assess changes. These findings can help assess the success of MPAs and guide monitoring and research activities within the region.